Camping and travel equipment have become quite sophisticated in that many conveniences once reserved for the home, are now available on recreational trips. Many of these conveniences, such as air conditioning, T.V., refrigerator, coffee pot, lights, toaster, fry pan, iron, radio and the like, are designed for operation by on-site generated electric current. Accordingly, electric generators are now provided as standard equipment for many of the new generation campers and trailers. It is not unusual for portable electric generators to be installed in other type vehicles, such as converted pick-up trucks, to power the same appliances as previously discussed.
Many of the electric generators are of the standard four cycle engine type and are fueled by gasoline or propane. As with any engine that operates from petroleum or petroleum derivatives, the exhaust is characterized by hot particulates, commonly carbon ash or sparks. In most areas of travel, it is highly desirable to prevent those hot particulates from entering the atmosphere. It is particularly crucial to prevent the particulates from being exhausted in woodlands or areas of flammable brush. In some areas, governmental regulations may require the use of a muffling device which prevents spark emission on electric generators. In recognition of the problem, the U.S. Department of Agriculture-Forest Service, provides testing of spark arresters to qualify under their standards.
Exhaust muffling and spark arrest in electric generators of the type described, present some unusual problems. In an ordinary automobile engine, there is a substantial distance between the exhaust outlet of the engine to the muffler at the rear of the car. This means that a spark or hot particulate may travel on the order of 12 to 17 feet and more before being exhausted or trapped in the muffler. During that travel, substantial cooling can take place, and the spark can burn itself out. In small electric generators, there is no such extensive travel possible because of the limited cabinet space. Therefore, the sparks must be trapped almost immediately upon being delivered by the engine into the muffler. There is no chance for the sparks to cool or burn out before being passed into the muffler or arresting device.
The prior art comprises a spark arrester characterized by a single chamber having a diagonal partition or screen. The screen is included to trap the hot particulates within the chamber to prevent their exhaust into the atmosphere. This system is not completely effective in removing all hot particulates from the exhaust. It is only necessary for a hot particulate to pass the small interface occupied by the screen to be in a position whereby it can be exhausted into the atmosphere. The particulates are often very small and are able to pass through even the finest mesh screen included in the muffling devices. Furthermore, the screen cannot be made with apertures that are too small, without greatly increasing the back pressure of the system and hindering the performance of the engine. It has been recognized that there is a need for a spark arresting device that is efficient in its filtering out of all hot particulates, and at the same time permits the generator to function at its peak efficiency.